The present invention relates to an improvement in skis.
Skis have been made of wood, FRP, fiber reinforced metals and other material.
Wooden skis frequently used in the past were in a keel-like shape and had an intermediate portion which is thickened in order to maintain strength. Since such skis are heavy, bad in maneuverability and insufficient in flexural rigidity, however, they have gradually been replaced with tabular skis, which are made of FRP or metals and excellent in performance. Skis generally used now have such a shape that, as shown in FIG. 1, the thickness of a ski 1 gradually increases from the ski front end portion to the central portion and then gradually decreases from the central portion to the rear end portion. That is, both the front and rear parts are tapered, and the intermediate upper surface of the ski 1 is flat. On the other hand, such structures are known as a sandwich structure in which, as shown in FIG. 2, reinforcing members 2 constituted by FRP plates or the like are disposed on the upper and lower surfaces of a core material or as a box structure in which a reinforcing member is disposed around the entire periphery of a core material.
These structures are generally employed by ski manufacturers, since they facilitate the ski manufacturing process.
In view of the physical properties of skis, however, it is exceedingly difficult to provide a design which gives an optimum balance of various interrelated properties, such as torsional strength, flexural strength, vibration damping property, air resistance and the like.
For example, if the torsional strength of a ski is improved, the flexural strength becomes higher to make the ski unfavorably rigid as well as to impair the vibration damping property, causing adverse effects on the sliding performance.
In addition, for reduction of the air resistance of a ski in sliding, a bore of any desired shape is opened in the shovel portion formed at the front end of a ski, or the rising degree of the shovel portion is decreased, thereby to suppress the air resistance as much as possible for increasing the speed in sliding. These methods, however, require much labor in the manufacturing process and a higher production cost.
Therefore, it has been desired to develop a ski improved to have a proper elasticity, a high torsional strength, an excellent vibration damping property and a small air resistance value through a combination of materials having various properties. Although various research and development work has been carried out, no satisfactory ski has been proposed yet.
In view of the above-mentioned disadvantages of the prior art, it is an object of the invention to provide a ski excellent in slidability through an improvement of the ski in various properties, such as rigidity, torsional strength, vibration damping and, air resistance, by replacing the conventional upper surface shape of the ski, which has been tabular, with such a shape that a roof-shaped projection is formed on the upper surface of the ski.